Enclosed switch with defeatable door interlock



June 8, 1965 L. A, HERCULES 3,188,410

ENCLOSED SWITCH WITH DEFEATABLE DOOR INTERLOCK Filed Aug. 26. 1960 5 Sheets-Sheet 1 44 J9 y f f) v rf) 23 '.23 uw 27%., 5\ Z 5 4g I f/.f

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3,188,410 ENCLOSED SWITCH WITH DEFEATABLE DOOR 'INTERLOCK Filed Aug. 26, 1960 June 8, 1965 A. HERCULES 5 Sheets-Sheet 3 ivm ya.

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United States Patent OY ENCLOSED SWITCH WITH DEFEAIABLE DGOR INTERLCK Lester A. Hercules, St. Louis, Mo., assigner to Frank Adam Electric Company, St. Louis, Mo., a corporation of Missouri Filed Aug. 26, 1960, Ser. No. 52,234 Claims. (Cl. 24th-5ft) This invention relates to fused operating switches for panelboards, switchboards, and the like, and more particularly to a fused switching Iunit wherein the fuses are enclosed behind a door with an interlock operated by the switch handle so as to prevent normal access thereto when the -switch is closed.

It will be understood that panelboards and switchboards are presently manufactured in predetermined sizes, and that the various units mounted therein to control branch circuits are also manufactured to predetermined or standardized dimensions. Such control units include circuit breakersQswitches, cover-operated fused disconnect switches and fused quick-break switches. This disclosure is particularly directed to the last category, it being understood that such fused switches are preferred in many industrial applications, because of the greater sensitivity of fuses, as compared with circuit breakers, and because of the superior circuit-opening action, as compared with cover-operated fused disconnect switches.

A fused quick-break switching unit of dead-front type has an external switch handle for operating the switch contacts and a hinged door for access to the fuses. The switch usually includes an overcentering spring mechanism to provide snap-acting contact operation and a door interlock is coupled to the switch handle (or switch mechanism) so that the door is locked when the switch handle is in its normal switch-closed position. The door interlock may incorporate a trick feature to permit opening of the door without opening the switch contacts by one who has been informed of the secret to defeating the lock, such a condition being desirable to permit skilled personnel to check the fuse and circuit without interrupting it.

Heretofore, such fused quick-break switching units have been relatively bulky and expensive in comparison with other types of control units. The conductive parts must be of a certain minimum size and spacing, depending upon the electrical rating of the unit. Also, the snap-action and door interlock mechanism present problems in achieving an economical compact unit, particularly in the smaller more popular sizes, such as the thirty and sixty ampere units.

Accordingly, the principal object of this disclosure is to provide an exceptionally compact and relatively inexpensive fused quick-break switching unit in the thirty and sixty ampere sizes, although certain features of the unit disclosed herein might be utilized in other types of control units. Among the more specific objects of the invention may be noted the provision of a one, two or three pole single or twin unit which affords manufacturing economies by utilizing pre-existing components presently manufactured in large volume and at low cost for other purposes; the provision of a unit which is readily assembled with a minimum of screw fasteners; the provision of a unit which has a minimum vertical Patented .inne 8, 1965 dimension, such dimension being significant in that it determines the number of units that can be mounted within a panelboard or switchboard of predetermined size; and the provision of a unit wherein the fuses are arranged in a novel particularly compact manner.

In the attainment of these objectives, brieliy, the switching unit herein disclosed comprises a main enclosure in the form of a trough having a length such as to fit within the horizontal dimension of the switchboard and a minimum vertical dimension (three inches for a threepole thirty ampere unit). IThis dimension permits twenty such units to be mounted within a panelboard having a vertical dimension of sixty inches. Previous units of the same electrical' capacity have been fty percent larger, with the result that considerably fewer units could be mounted in the panelboard.

End panels are secured to the ends of the trough in a y novel manner without the use of screws, rivets or the like,

and the back portions of the end panels are adapted as a means of attaching the unit within the panel. A door is attached to the front of each panel to extend over a front of the trough-like enclosure, and the center space between the doors is covered with a panel carrying a pair of switch handles and associated door interlock mechanism. Switches are mounted behind the front panel for operation by the door interlock mechanism and fuse holders are mounted endwise of the switches behind the doors.

In accordance with the present invention and for reasons of economy, pre-existing circuit breaker parts are utilized in making the switches. It will be understood that thirty and sixty ampere circuit breakers are in wide use, such units typically having an insulating housing measuring slightly less than an inch in Width and several inches in length and depth. Accordingly, three units may be mounted side by side in a three inch space to provide a three-pole switch. The insulating housing of each circuit breaker has an operating handle projecting from the front, a plug-on terminal at one end and a line terminal at the other end. The housing of a circuit breaker includes overcentering spring mechanism and contacts operated thereby. A circuit breaker would also include thermal responsive and magnetic elements for opening the contacts in response to an overload, but these elements are omitted from the units utilized herein. Also, the line terminal is replaced with a plug-on terminal for connection with the fuse holders.

An insulator carrying bus-bar stabs is mounted on the back wall of the trough enclosure centrally thereof so that stabs project rearwardly for plug-in connection with vertical bus bars mounted on edge in the back of a panelboard. Plug-in blades connected to the stabs and supported on the insulator project through an opening in the back wall of the enclosure for plug-in connection with the terminals at the inner ends of the switches, which are in substantial abutting relationship. Fuse-holding insulators are mounted endwise of the switches, and each insulator carries fuse clips on its front surface. Fuse clips at the inner end of the insulator are connected to blades which project inwardly for plug-in connection with the terminals on the outer ends of the switches, whereas the outer clips are connected to load terminals, so that branch circuits brought in through an opening in the end panel are readily connected thereto. The central set of fuse clips is disposed on a line parallel to the side wails of the enclosure, and the inner clip is located loutwardly from the opposite circuit breaker housing. The outer pairs of fuse clips are located on lines diverging outwardly with respect to the circuit breaker housings with the inner clips of each set being located generally between the inner central clip and the outer ends of the switches. The outer clips of the outer sets are located generally opposite the inner clip of the central set. This angular disposition of the outer fuse clips is advantageous in providing the necessary separation between conductive parts of different polarity in a minimum space, and also in providing sutiicient space to permit insertion of a fuse puller. n

The handles of switches mounted side by side may be connected together by a rod. A channel-like member is slidably mounted on the vback surface of the front center panel, and flanges on this member' are notched to vstraddle the rod. The external handle is coupled by a crank to reciprocate the channel member and thereby operate the switches.

A d oor latch lever is pivoted on the back surface of the front panel and has a latch hook formed on its outer end, which hook cooperates with the inner edge of the opposite door to releasably retain the door in its closed position. The'door is released by moving the latch against the bias of a spring. An interlock condition is achieved by forming a lug to project from the lever (in spaced relationship from its pivotal axis) for cooperation with a part of the channel member or a part carried by the channel member. Accordingly, the channel member may lock the latch lever when reciprocated to its switchon position. A defeatable door-interlock condition is achieved by mounting a plate upon the channel member for relative repicrocation, this plate being cooperable with the latch lug in the normal switch-on position. The external handle then has a lost-motion connection with the channel member and a direct connection with the second plate. The plate is normally spring biased on the channel member to a door locking position, but the plate Vcan be reciprocated (within limits) relative to the channel member may be manually pivoted clear of the door. The

arrangement of parts is advantageous in that they can be readily assembled without screws, by securing the channel member and second plate with hairpin springs,

which fit on studs over the back surfaces of the respective elements.

A U-shaped strap is snapped between the side Walls of the enclosure at the front central portion to lock the circuit breaker housings, and the side walls of the housing are then being secured against outward displacement (to prevent displacementof the stirrup) by flanges on the front panel. The front panel is secured by one or more screws extending therethrough into the strap. This is oner of the few screws in the unit. Another screw or two would be utilized in aiiixing the stab and fuse insulators to the back wall of the enclosure.

Other features of the invention will be in part apparent from and in part pointed out in the following detail description taken in connection with the accompanying drawings,pin which:

FIG. l is a frontelevation of a twin three-pole unit as viewed `from the front of a panelboard, switchboard or the like;

FIG. 2 is a bottom elevation of the unit shown in FIG. 1;

FIG. 3 is an end elevation of the -unit shown in FIG. l;

FIG. 4 is a cross-section, on an enlarged scale, taken generally on the line 4-4 of FIG. 2;

FIG. 5 is an enlarged longitudinal cross-section taken generally on the line 5 5 of FIG. 3;

FIG. 6 is a longitudinal section taken generally on the line 6-6 of FIG. 5;

FIG. 7 is a detail section taken generally on the line '7 7 of FIG. 5 illustrating the door interlock mechanism in the switch-off position;

FIG. 8 is a view similar to FIG. 7 illustrating the parts in a switch-on position, and with the door latch locked;

FIG. 9 is a view similar to FIG. 8, but illustrating the parts moved to a position for opening the door with the switch on;

FIG. 10 is a cross section taken on the line ltr-1t) of FIG. 8; and

FIG. 11 is a detail cross section of an external operating handle. Y

Referring to the drawings, there is shown a troughshaped main enclosure having a back wall 1 and side (or top and bottom) walls 3. This trough enclosure is of a length corresponding approximately to the width of the opening in a panel-board and is a twin unit. The trough is adapted to be mounted within the panelboard upon end panels 5, secured to the ends of the trough. The upper portions of the side walls are offset inwardly at angled steps 7, and openings 9 are formed in the steps adjacent the ends thereof. Another opening or recess 11 (FIG. 5) is formed at each end of the back wall of the enclosure. YFlanges'l3 on the end panels slip between the side walls 3, and upper hook-like tongues I5 extend outwardly of ythe side walls to engage within the openings 9. A lower vtongue I7 is formed on the end panel opposite the opening 1l to seat therein. Accordingly, the end panels are readily assembled, without screws, by pushing a panel .inwardly and thence downwardly to'interlock its tongues within the corresponding openings. The panel is then y locked in position by bending a tongue 2l (FIGS. 3 and 5) inwardly from opening l@ beneath the bottom wall l, thereby to prevent upward displacement of the end panel. The lower portion 23 of each end closure member is bent `Voutwardly to form a foot which may have screw holes for securing the unit on a panclboard.

The panelboard (not shown) would have a set of bus bars extending vertically behind the center portions of the switching units, and the lparticular unit Vdisclosed herein is of the plug-in type in that it incorporates stabs Z5 projecting rearwardly from the back of the unit for plugin connectionwith the bus bars. The stabs 25 are secured upon an insulator 27 in staggered relationship, and the insulator is fastened to the back wall 1 by screws 29.

There are three stabs spaced fromone another longitudinally and transversely, and ribs 3l project from the insulator between the stabs to provide proper electrical spacing. Each stab 25 has a base part 34 secured against a conductive element 33 by a screw, and a blade 37 is b ent from the element 33 to project through the insulator and an opening 3S in the back of the enclosure for plugin connection with the switches to be described.

The front of the unit is closed by a pair of fuse-access doors 39 having flange portions 4l, which t about the inset upper margins of the side walls. The doors are secured to hinges 44, and the hinges are fastened Vto the en d panels 5. yA central front panel 43 having side flanges Vi5 is fixed by screws 4'7 in the space between the two doors 39. The flanges 45 ofthe fixedpanel are notched at 46 to act as door stops for the doors, this arrangement being advantageousVV in assuring .a smooth even front-when the doors are closed. The panel 43 carries switch-operating handles A49, there being ,twoY such handles for a twin unit. The handles operate switching mechanism and door interlock mechanism carried behind lthe panel V43. The fuses are located behind the doors 39, and switches are located between the fuses behind the panel 43.

In accordance with this invention, the switches are selfcontained devices in the form of standard circuit breakers without the usual magnetic thermal responsive overload mechanism. It will be understood that circuit breakers in the thirty and sixty ampere rating are economical because of the volume manufacture permitted by their wide use, but in some industrial applications, the overload protecting mechanism of a circuit breaker lacks suicient sensitivity, hence the necessity for a fused condition. Where a quick make and break switch is required as in many fused switches, it is necessary to provide special contacts and a snap-.acting or overcentering switch mechanism for operating the contacts. Since this mechanism is incorporated Within existing standard circuit breakers, the invention contemplates the use of standard or modified circuit breaker parts including the housing, contacts and operating mechanism, but without the overload-responsive parts. The details of the circuit breaker are not important to the present disclosure. Such details are disclosed in numerous prior patents on circuit breakers and it will be readily apparent to those skilled in the art how circuit breaker parts can be used as switches.

The housing 5l of a typical circuit breaker (thirty or sixty amperes) measures about one inch in thickness, three inches in length and two and one-half inches in depth. These dimensions apply to a single-pole circuit breaker, and in accordance with this invention, one, two or three such housings are assembled side by side to form a one, two or three pole unit. A toggle-like handle 53 projects from the forward portion of each housing to operate the internal contacts, and the several handles are operated by the main external handles 49.

Most circuit breakers are designed for plug-in connection with bus bar terminals of a panelboard, and the devicesillustrated herein have terminals 55 at their inner ends, which make a plug-in connection with the blades 37 referred to previously. In a twin three-pole unit, there are two sets of housings, each set having three housings. The two sets of housings are in substantial abutting relationship at their inner ends, so that the terminals 55 of a pair of opposite circuit breakers sharethe same blade 37.

In a conventional circuit breaker, a screw terminal is usually provided at the opposite end for connecting a branch circuit wire, but the present invention contemplates that a plug-in terminal 57 will be substituted for the usual screw terminal. The terminal 57 cooperates with a blade of a fuse-holder assembly (FIG. 5). The fuse-holder assemblies are located at the ends of the housing behind the doors 39. The terminals 55 and 57 in each circuit breaker are of the clip-type and are recessed, the cooperating blades being accommodated through openings in the back and end Walls of the housings 5l.

A fuse-holder assembly comprises an insulator base 6l molded from plastic or the like and secured against the back wall l ofthe enclosure by screws 63. A folded sheet of insulating material 65 is inserted within the enclosure to lie against the back and side walls. Similar insulating members 67 may be secured to the end panels 5.

One of the objects of the disclosure is to provide all of the necessary components for a three-pole thirty ampere unit within a dimension of three inches (side wall 3 to side Wall 3), while permitting removal of the fuses with a fuse puller. The objective is herein met by the particular arrangement of the fuses illustrated in FIG. 6. The three fuses are shown at Fl, F2 and F3, the fuse F1 being located along a center line and the fuses F2 and F3 vbeing angled with their inner ends adjacent one another and their outer ends spread apart to lie on opposite sides of the fuse F1. The insulator 6l is formed with a U-shaped wall 69 extending about the inner end of fuse F1, thereby to isolate it from fuses F2 and F3. A second insulating wall 71 extends between the inner ends of fuses F2 and F3. Accordingly, the fuse Fl might be gripped by a fuse puller inserted outwardly of the wall 69, whereas either of fuses F2 or F3 is gripped by a puller inserted between the walls 69 and 7l. The angled relationship of fuses F2 and F3 is essential to provide space for accommodating the puller.

The inner and outer terminals for the fuses F 1, F2 and F3 are indicated at Tl, T2 and T3, respectively, and at llt) d Tl, T5 and T6, respectively. The inner terminal Tl for fuse Fl is secured upon a blade-like element 73, which extends through an opening '74 into a back recess 76 inwardly for plug-in connection with the outer clip 57 of the central switch Sl. T he terminals T2 and T3 are seated upon similar blade-like elements which extend through openings to the back portion of the insulator and thence inwardly for plug-in connection with the terminals 57 of the switches S2 and S3. The outer fuse terminals T4, T5 and T6 are seated upon wire terminals 77, 78 and 79, respectively, which project endwise opposite an opening 8l (FlG. 3) in the end wall 5 of the enclosure. The branch circuit cables are inserted through this opening and connected to the terminals.

The switch housings 5l are locked against the black wall of the enclosure and the inner ends of the fuse-holder insulators by a cross strap or bar 75 (FIG. 4). The transverse portion of part 75 overlaps the front surfaces of the switch housings and the ends of the part are secured by detents 77 on ends of the strap, which detents seat on dents formed in the side walls of the enclosure. The side walls spring outwardly a slight amount when the strap is inserted, and are then secured against outward displacement by the flanges d5 of the fixed front panel 43 applied subsequently. The screws 47, which secure the front panel 43, are threaded into the part 75 and act as stops for detents 77 on the ends of the strap, thereby to prevent inward displacement of the strap ends.

The several toggle handles 53 in a row (which makes up a three-pole switch) are connected for common actuation by a transverse rod 8l extending therethrough. A channel switch-operating member 83 (FIG. 4) straddles the center handle 53, and the side flanges of part S3 are formed with notches d5 (FlGS. 5 and 7) to receive the rod 8l. The toggle handles 53 are thereby actuated upon reciprocating movement of member 83.

The channel member S3 is mounted for sliding movement on the back surface of the front panel 43 and is reciprocated by the external handle 49. Referring to FIG. l1, a circular opening 87 is cut in the panel 43 to accommodate a disc S9. A U-shaped member 91 projects forwardly from the disc S9, and the handle 49 is secured thereto by a screw 93. An eccentric plate 95 is then secured to the bottom surface of the disc 89 to provide a bearing vfor the handle 49, and a crank pin 97 projects rearwardly Ifrom the eccentric 95 within an opening 99 in the channel member 83. The journal 87 may be formed with one or more notches lill projecting radially for cooperation with a locking bar 103 (FIG. l1). The bar is spring biased at 165 out of the notches ll but can be pulled outwardly into one of the notches lill and secured with a padlock (not shown), which is accommodated at 107 in the bar 103. The locking bar permits the switch to be padlocked in either its switchon or switch-olf position, there being a suitable notch lill opposite each position of the switch handle 49.

The associated door 39 is locked by a latch lever lll having a latch hook 1l3 projecting forwardly. The hook 113 extends through a recess 115 in the inner end of the door and is movable into overhanging locking relationship with the door. The latch lever is pivoted upon a stud l to extend across the back surface of panel 43. At its inner end, the latch lever is provided with a hook M9 receiving one end of a double hairpin spring 122i. Stud M7 is fixed in the panel 43 and is formed with a groove 118 (FlG. 10). The spring 121 is bent around the stud within the groove, and holds a washer l2@ against the part S3. The spring serves both latch levers of the twin unit and also functions as a retaining member for the latch lever and channel member, thereby simplifying assembly of the parts.

The channel member 33 extends across the eccentric 95 and latch lever lll and a slot 123 (FIG. 9) is cut in one end of the channel member to accommodate the stud lll. A slot ll25 is cut at the other end and accommodates alessio i? a second stud 127, also fixed upon the panel 43, hence channel element 83 is guided for reciprocation by the studs.

The latch lever has a locking lug 129 upset therefrom for cooperation with either the channel member 83 or a second plate 131, which is carried by the channel member. if a door interlock without a defeatable feature is desired, the channel member 83 may be the means of holding the latch lever in its door locking position when the switch is closed. When the channel member is retracted to the switch-off position of FIG. 7, it is clear of the lug 129 and the latch element may be manipulated to release the door. When the channel member is reciprocated -to the switch-on position (FIG. 8), it could move into locking engagement with the lug 129 to secure the latch lever against manipulation. This condition is not shown herein, but the necessary operation is achieved merely by providing a slot of proper shape at the outer end of the member opposite the latch lug 129.

The mechanism disclosed includes a defeatable door interlock in the form of a second plate 131, which is cut with a keyhole recess 133 at its outer end for cooperation with the lug 129. A similar recess 135 in the channel Ymember is of a shape such as to clear the latch lug 129 in both the switch-on and switch-off positions (compare FiGS. 7 and r8). The plate 131 is slidably guided on the channel member 83 by its flanges 136 and is spring biased against the crank pin 97 (FIGS. 7 and 8) by a hairpin spring 137. One leg 139 of the spring is mounted and extends through keyhole openings 141 (FIG. 5) in the sides of the channel member, so as to be retained therein, while the other leg is caught beneath a lug 143 on plate 131. Accordingly, the spring 137 is a retainer for plate 131, thereby simplifying assembly.

When the main handle is moved to the switch-on posi tion (FIG. 8), the recess 133 in the plate 131 engages with the sides of the locking lug 129 to lock the door "latch lever. A defeatable interlock condition is achieved 'by making the crank pin hole 99 relatively large, so as to provide a lostmotion connectionV between the crank pin and channel member. The external handle 49 may then be moved a limited distance beyond the switch-on position (FIG. 9) to move the plate 131 (relative to the 'channel member) to a position wherein the opening 133 is clear of the locking lug 129, thereby releasing the door Alatch lever. The channel member does not move, being retained by the toggle handles ?.Y Since the external handle must be moved from its normal switch-on posi- A.tion in order to release the door latch, the way of defeating the interlock would not be known, except to those that were informed of the secret.' FIGS. 7-9 also illustrate how the plate 131 may have a crank pin opening 145 adjacent the crank pin opening 99. When the defeatable interlock action is not desired, the plate 131 is positioned during assembly so that the crank pin 97 projects through the opening 145. Alternatively, the plate 131 may be locked to channel member 83, as by a screw (not shown).

Changes in and modifications of the construction described may be made without departing from the spirit of my invention or sacrificing its advantages.

Having thus described the invention, what is claimed and desired to be secured by Letters Patent is:

1. In a fused switching unit, the improvement that comprises an enclosure having back and side walls and an open front, a door hinged at one end of the enclosure to extend partially across the front opening, fuse holders mounted within said enclosure behind Said door, a panel kfixed to the front of said enclosure adjacent the free end of said door, a switch handle pivoted on the outer surface of said fixed panel, a switch mounted within the enclosure ,in spaced relationship behind said xed panel, a door latch member movably mounted behind said xed panel, said latch member having a part exposed for manipulation from the exterior of said panel and door, a switchoperating member movably mounted behind said fixed panel for actuation by said switch handle and for actuation lof said switch, and interlock means actuated by said switchoperating member and cooperable with said door latch member to lock the door latch member when the switch handle is in its switch-closed position, said interlock means comprising an interlock member mounted upon said switch-operating member for movement relative thereto, crank means actuated by the switch handle for actuating said switch-operating member and having a lost-motion connection therewith, so as to permit limited relative movement between the handle and switch-operating member in the switch-on condition, said crankmeans havinga direct connection with the interlock member, thereby to permit movement of the interlock member clear of the latch member in the switch-on condition.

2. in a fused switching unit, the improvement that comprises an elongate enclosure of U-shaped cross-section, a door hinged at one end of the enclosure to extend partially across the front opening thereof, fuse holders mounted within said enclosure behindsaid door, a panel iixed t0 the front of said enclosure adjacent the free end of said door, a switch-operating handle pivoted on the outer surface of said fixed panel, a switch mounted within said enclosure behind said xed panel, a door latch lever pivotally mounted on the inner surface of said iixed panel and having a latch hook cooperable with the door, a switch-operating member movably mounted on the fixed panel in position to actuate the switch therebehind, crank means interconnecting said handle and switch-operating member, and an interlock member `mounted upon said switch-operating member for movement relative thereto, said crank means having a lost-motion connection with said switch-operating member to permit limited relative movement between said handle and said switch-operating member when the handle is in its switch-on position, said crank means having a direct connection to the interlock member, thereby to permit movement of the interlock member clear of the latch lever with the switch-operating member in its switch-on position.

3. In an enclosed switching unit, the improvement that comprises a front panel, a stud projecting rearwardly from said front panel, a latch lever pivotally mounted on said stud and extending along the back surface of said panel, aswitch-operating member mounted for slidable movement relative to the latch lever and having a slot through which said stud projects to guide the switch-operating member, said switch-operating member having spaced anges, said stud being formed with a groove, a hairpin spring releasably secured within said groove and within a part of said latch lever, whereby said spring serves both as biasing means for the latch lever and a retainer for both the latch lever and switch-operating member, and a second hairpin spring secured in said iianges 4and interlock element in overlying relationship with the interlock element, whereby said second hairpin spring retains the interlock element upon the switch-operating member and biases the interlock element relative to the switch-operating member.

4. The improvement in an enclosed switching unit as set forth in claim 3, wherein said latch lever is formed with` a rearwardly projecting locking lug, and said interlock element has a part movable into and out of locking cooperation with said lug.

5. The improvement in an enclosed switching unit as set forth in claim 4, having a crank plate mounted between the switch-operating member and the fixed panel,

Va crank pin projecting rearwardly from said crank plate,

Vbeing biased into engagement with said crank pin, thereby yto permit limited movement of the interlock element relacrank pin.

References Cited bythe Examiner UNITED STATES PATENTS Burns 200-50 Broadwell 200-50 Olofson 200-50 Cole 200-50 Murray 200-168 Robertson 200-50 Frank 200-168 Johnson 200-50 10 Duvall et al 200-50 Hercules 200-50 Brown 200--50 Benedicts 200-50 Cole 200-50 Groves et al 200-50 Norden 200-50 Rexroad 200-50 Chace 200-50 BERNARD A. GILHEANY, Primary Examiner. MAX L. LEVY, ROBERT K. SCHAEFER, Examiners. 

1. IN A FUSED SWITHCING UNIT, THE IMPROVEMENT THAT COMPIRSES AN ENCLOSURE HAVING BACK AND SIDE WALLS AND AN OPEN FRONT, A DOOR HINGED AT ONE END OF THE ENCLOSURE TO EXTEND PARTIALLY ACROSS THE FRON OPENING, FUSE HOLDERS MOUNTED WITHIN SAID ENCLOSURE BEHIND SAID DOOR, A PANEL FIXED TO THE FRONT OF SAID ENCLOSURE ADJACENT THE FREE END OF SAID DOOR, A SWITCH HANDLE PIVOTED AN THE OUTER SURFACE OF SAID FIXED PANEL, A SWITCH MOUNTED WITHIN THE ENCLOSURE IN SPACED RELATIONSHIP BEHIND SAID FIXED PANEL, A DOOR LATCH MEMBER MOVABLY MOUNTED BEHIND SAID FIXED PANEL, SID LATCH MENBER HAVING A PART EXPOSED FOR MANIPULATION FROM THE EXTERIOR OF SAID PANEL AND DOOR, A SWITCH-OPERATING MEMBER MOVABLY MOUNTED BEHIND SAID FIXED PANEL FOR ACTUATION BY SAID SWITCH HANDLE AND FOR SAID SWITCHSAID SWITCH, AND INTERLOCK MEANS ACTUATED BY SAID SWITCHOPERATING MEMBER AND COOPERABLE WITH SAID DOOR LATCH MEMBER TO LOCK THE DOOR LATCH MEMBER WHEN THE SWITCH HANDLE IS IN ITS SWITCH-CLOSED POSITION, SAID INTERLOCK MEANS COMPRISING AN INTERLOCK MEMBER MOUNTED UPON SAID SWITCH-OPERATING MEMBER FOR MOVEMENT RELATIVE THERETO, CRANK MEANS ACTUATED BY THE SWITCH HANDLE FOR ACTUATING SAID SWITCH-OPERATING MEMBER AND HAVING A LOST-MOTION CONNECTION THEREWITH, SO AS TO PERMIT LIMITED RELATIVE MOVEMENT BETWEEN THE HANDLE AND SWITCH-OPERATING MEMBER IN THE SWITCH-ON CONDITION, SAID CRANK MEANS HAVING A DIRECT CONNECTION WITH THE INTERLOCK MEMBER THEREBY TO PERMIT MOVEMENT OF THE INTERLOCK MEMBER CLEAR OF THE LATCH MEMBER IN THE SWITCH-ON CONDITION. 